A work machine, such as a construction, agriculture or forestry work machine typically includes a power unit in the form of an internal combustion (IC) engine. The IC engine may either be in the form of a compression ignition engine in which the heat of compression ignites timed and quantity selected fuel for combustion or a spark ignition engine in which a homogenous mixture is ignited by an ignition source or a homogenous charge compression ignition engine which is a hybrid of the former two. For most heavy work machines, the power unit is in the form of a diesel engine providing better torque, power and durability characteristics for work operations.
The emissions regulations set forth in the original Environmental Protection Agency (EPA) laws have initially been applied to on highway vehicles. In recent years, the EPA regulations have been applied to off-highway vehicles such as work machines. The issues faced by on-highway diesel engine applications are now being faced by off-highway applications.
In the usual applications, this requires an exhaust aftertreatment device which receives the products of combustion from the internal combustion engine and treats it appropriately to remove a combination of nitrous oxides, particulates and other hydrocarbons. These devices inherently require periodic regeneration to remove particulates or carbon matter so as to restore the aftertreatment device to a substantially new condition. This is necessary to maintain the effectiveness of treating the products of combustion so as to maintain both the letter and spirit of the EPA laws.
The issue of regeneration becomes difficult when applied to work machines in the sense that the machines are constantly being utilized to perform an industrial or agricultural function. Any regeneration effort must not prevent continued operation of the machine so that it can achieve its intended purpose, namely the industrial or agricultural function.
A number of efforts have been made to achieve regeneration and these include raising the temperature of the products of combustion to the exhaust aftertreatment device sufficiently so that any extra carbon is burned off. The devices to achieve this can be heaters, ultrasonic devices and adding hydrocarbons to the exhaust stream to achieve the temperatures required for regeneration.
Unfortunately, all of these approaches require energy beyond that necessary for the particular duty cycle of the work machine. In particular, adding hydrocarbons in the form of fuel decreases the fuel efficiency and therefore the effectiveness of the work machine. Devices incorporating heaters or ultrasonic devices require additional power sources to drive the temperature increasing function. Nowhere is the need for efficiency greater than in an agricultural machine having a duty cycle that varies between one of maximum load and such as driving a combine through a field and simultaneously harvesting, collecting and processing the harvested agricultural material. The opposite of this maximum load is the time in-between actual harvesting when the engine is operating at a small fraction of the maximum power available to the device.
What is needed in the art therefore, is a work machine that utilizes internal combustion engines and which efficiently and effectively regenerates exhaust aftertreatment devices associated with the internal combustion engines.